Is it possible for a triangle to have the side lengths of 3, 8, and 13

No

Step-by-step explanation:

The longest side of a triangle must be less than the sum of the shorter two sides.

3 + 8 = 11.  13 is not less than 11.  So it is not possible for a triangle to have these sides.

- 2 + 10x³ - 21x² + 19x - 4

step-by-step explanation:

each term in the second factor is multiplied by each term in the first factor

x²(- 2x² + 4x - 1) - 3x(- 2x² + 4x - 1) + 4(- 2x² + 4x - 1) ← distribute

= - 2 + 4x³ - x² + 6x³ - 12x² + 3x -8x² + 16x - 4

collect like terms

= - 2 + 10x³ - 21x² + 19x - 4 ← in standard form